The goal of our research is to uncover the neuronal mechanisms that limit the development of visual performance in primates. Recent advances in visual psychophysics and theory have made it possible to formulate questions about visual development in the same terms used to analyze adult vision, and we propose experiments to explore the neurobiology of development in these functional terms. We plan two main groups of experiments. First, we will study the development of the mechanisms supporting spatial vision, using modem methods to assess the components of visual efficiency using noise masking techniques. We win apply these methods to behavioral studies, and to electrophysiological studies of neurons in the LGN and striate cortex. In combination with a direct analysis of retinal structure in the same experimental animals, these methods should allow us to separate and evaluate the peripheral and central factors that limit the development of spatial vision. Second, we will use a combination of behavioral, electrophysiological and neuroanatomical methods to explore the development of the extrastriate cortical mechanisms that support the processing of visual motion. We will again use signal-in-noise techniques to measure the development of behavioral sensitivity to motion, and use the same techniques to study neurons in the striate cortex and in MT, an extrastriate area believed to be critically involved in motion processing. We will also explore the development of a form of motion signalling known to depend on intrinsic computations within MT, and the development of smooth pursuit eye movements, known in adults to depend on signals in MT. These functional studies will be complemented by neuroanatomical experiments designed to. explore the development of the functional connections and architecture of the extrastriate pathways leading to MT, and of the architecture of MT itself Taken together, the experiments will provide unified accounts of the biological and behavioral processes whose development determines these two important components of adult visual function. Future work will build on these results to provide accounts of the alterations of development that lead to amblyopia, and to explore the development of other functions dependent on cortico-cortical interactions.